Dry etching

Dry etching refers to the removal of material, typically a masked pattern of semiconductor material, by exposing the material to a bombardment of ions (usually a plasma of reactive gases such as fluorocarbons, oxygen, chlorine, boron trichloride; sometimes with addition of nitrogen, argon, helium and other gases) that dislodge portions of the material from the exposed surface. A common type of dry etching is reactive-ion etching. Unlike with many (but not all, see isotropic etching) of the wet chemical etchants used in wet etching, the dry etching process typically etches directionally or anisotropically. Dry etching is used in conjunction with photolithographic techniques to attack certain areas of a semiconductor surface in order to form recesses in material. Applications include contact holes (which are contacts to the underlying semiconductor substrate), via holes (which are holes that are formed to provide an interconnect path between conductive layers in the layered semiconductor device), transistor gates for FinFET technology, or to otherwise remove portions of semiconductor layers where predominantly vertical sides are desired. Along with semiconductor manufacturing, micromachining and display production, the removal of organic residues by oxygen plasmas is sometimes correctly described as a dry etch process. The term plasma ashing can be used instead. Dry etching is particularly useful for materials and semiconductors which are chemically resistant and could not be wet etched, such as silicon carbide or gallium nitride. Low density plasma (LDP) is able to produce high energy reactions at a low energy cost in thanks to its low pressure, meaning dry etch requires a relatively small quantity of chemicals and electricity to function. Additionally, dry etch equipment tends to be an order of magnitude cheaper than photolithography equipment, so many manufacturers rely on dry etching strategies such as pitch doubling or quartering to gain advanced resolutions (14nm+) while needing less advanced photolithography tools.